This invention generally relates to solar energy collectors. More specifically, this invention relates to solar energy collectors using double-walled glass tubes which are the major energy collection elements. Precisely, this invention relates to a solar energy collector of the type described which includes a heat exchanger in a gas filled manifold to allow use of air as an energy collection medium without requiring bulky air duct-work.
Most solar energy collectors of the prior art are of the flat plate type wherein air or water is circulated to absorb solar energy. Despite some advantages of flat plate collectors, glass, tubular collector arrays offer manufacturing and installation economies, In addition, air has seldom been used as the medium for extracting the solar energy from the collector array, whatever the type, for a number of reasons. If air is to be used to convey the solar energy elsewhere within a building for utilization, a bulky and expensive duct-work system is required. In addition, large volumes of air must be moved which require significant energy for pumping power. Flat plate collectors which use water for energy collection also have some deficiencies. The amount of water on the roof at any time is significant, thus creating a weight load factor problem. Water in such large quantities in a thin film is subject to freezing, unless anti-freeze solutions are used. A leak in such a system would liberate a large quantity of water on the roof where seepage into the structure could become a problem. In addition, these systems can seldom meet boiler codes, so the advantages inherent in operating at elevated pressures are not available. We have invented a solar energy collector which has a plurality of double-wall glass tubes connected to a manifold on the roof of a building. Air is circulated through the tubes and manifold to be heated by the sun. The pumping power and volume of air flow are relatively small. A heat exchanger carries water through the manifold. The water is heated by the circulating air. There is, therefore, only a small amount of water on the roof at any time, the heat exchanger can meet boiler codes, and the heated water may be transported within the building for utilization in relatively small water pipelines. Examples of the prior art may be seen in the following U.S. Pat. Nos. 1,242,511; 1,338,644; 2,342,211; 2,469,496; 2,601,905; 2,680,565; 2,933,885; and 3,799,145.